Have held back this speculation till now. There may be many Corona varieties around that have never been identified and do not cause significant symptoms but cross react in some tests or give a degree of immunity to people who are exposed. We are still in the early phase of understanding DNA and RNA science.
There may be many Corona varieties around that have never been identified and do not cause significant symptoms but cross react in some tests or give a degree of immunity to people who are exposed.
Roughly 80% of cases of the common cold are caused by roughly 200 strains of rhinovirus. Most of the remainder are caused by coronaviruses. That said, there are some flu-causing coronaviruses like the Wuhan coronavirus, SARs and MERS. The Wuhan coronavirus is similar to the other two named there, but far more infectious, and rather less lethal per infection (SARS 10-12%, MERS 30-35%, COVID-19 as reported in China 3.9-4.5%).
There might be an individual strain of coronavirus which causes some cross-immunity, but in general pretty much everyone world-wide has been exposed to at least some form of coronavirus.